The present invention relates to a method for mounting an electronic component on a substrate and an apparatus for implementing the method, and particularly to an electronic component mounting apparatus provided with a recognizing means of inexpensive construction which is capable of recognizing electronic components of various sizes during they are moved.
A known conventional electronic component mounting apparatus is constructed such that a mounting head driven for movement by a driver holds an electronic component at a feed station, and pauses at a particular position of a recognition station where the electronic component is monitored with a recognizing camera before being moved to a mounting station, where the electronic component is precisely positioned and mounted on a substrate.
However, in such a construction, the mounting head has to be paused each time at the particular position of the recognition station for recognition of the electronic component, thus increasing the mounting tact and limiting the improvement of productivity.
For overcoming such a drawback, a modified electronic component mounting apparatus employs a line camera with a one-dimensional CCD array as the recognition camera, with which an image of electronic component held with the mounting head being moved is picked up for recognition of their held location.
Another modified apparatus is known which employs a shutter camera for taking a two-dimensional image of electronic component held with the mounting head being moved to monitor their location.
Line cameras having a one-dimensional CCD array has an advantage of high resolution in comparison with other types of cameras and thus are suitable for taking images and recognizing components of large size with high accuracy. When taking images with a line camera, in order to maintain the ratio of length to breadth of the image, it is necessary to move an object of which image is being picked up in a direction vertical to the lengthwise direction of the arrangement of the CCD by a distance which is equivalent to a length of the object assigned to each pixel of CCD during the scanning action of one line. The higher the resolution is needed, the shorter the distance of moving the object within a period of transfer of one line is decreased. Moreover, as the transfer of an image data with thousands of pixels from the CCD takes a considerable length of time, the moving speed of the electronic component above the line camera cannot be increased.
Theoretically, shutter cameras may have better capacity of taking images at a high speed due to the emission of a light with high brightness in a short time by utilizing their shutter function. However, since a common two-dimensional CCD array which is applicable to image taking at a high speed comprises about 500.times.500 pixels and has a field of view bound in extension, the size of electronic component as the object to be monitored is limited in order for maintaining the resolution power above a certain level.
There are actually high-speeded line cameras or cameras of high resolving power having a sensor with 2000.times.2000 pixels and being capable of scanning at 60 MHz, but their prices are exorbitant and thus they cannot be applied to such a field as the electronic component mounting devices.
In view of the foregoing, it is an object of the present invention to provide an electronic component mounting method and an apparatus of inexpensive construction for implementing the method, by which it is possible to accurately recognize various sizes of electronic components which are being moved for precise mounting on to a substrate.